Cooled Dielectrically Buffered Microwave Dipole Antenna

ABSTRACT

Microwave antenna assemblies incorporating a resilient insulating coupler are described herein. The microwave antenna includes a radiating portion connected by a coaxial feedline to a power generating source, e.g., a generator. Distal and proximal radiating portions of the antenna, which correspond to inner and outer conductors provided by the coaxial feedline, are separated by the resilient insulating coupler. The described coupler includes a proximal threaded portion, and an overmolded insulating portion formed from an elastomeric material. The inner conductor of the coaxial feedline is joined to the threaded portion of the coupler, and is placed under tension to draw together the distal radiating portion, the coupler, and the proximal radiating portion into a single rigid assembly. In use, the resilient coupler provides increased strength and reliability by absorbing mechanical stresses typically encountered during microwave ablation procedures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent application Ser. No. 12/401,268 entitled “Cooled Dielectrically Buffered Microwave Dipole Antenna” filed on Mar. 10, 2009 and hereby incorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave surgical devices having a microwave antenna which may be inserted directly into tissue for diagnosis and treatment of diseases. More particularly, the present disclosure is directed to a microwave antenna having a cooled distal tip and a method of manufacturing the same.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures (which are slightly lower than temperatures normally injurious to healthy cells.) These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, liver, lung, kidney, and breast.

One non-invasive procedure generally involves the treatment of tissue (e.g., a tumor) underlying the skin via the use of microwave energy. The microwave energy is able to non-invasively penetrate the skin to reach the underlying tissue. However, this non-invasive procedure may result in the unwanted heating of healthy tissue. Thus, the non-invasive use of microwave energy requires a great deal of control.

Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical. One type is a monopole antenna probe, which consists of a single, elongated microwave conductor exposed at the end of the probe. The probe is typically surrounded by a dielectric sleeve. The second type of microwave probe commonly used is a dipole antenna, which consists of a coaxial construction having an inner conductor and an outer conductor with a dielectric junction separating a portion of the inner conductor. The inner conductor may be coupled to a portion corresponding to a first dipole radiating portion, and a portion of the outer conductor may be coupled to a second dipole radiating portion. The dipole radiating portions may be configured such that one radiating portion is located proximally of the dielectric junction, and the other portion is located distally of the dielectric junction. In the monopole and dipole antenna probe, microwave energy generally radiates perpendicularly from the axis of the conductor.

The typical microwave antenna has a long, thin inner conductor that extends along the axis of the probe and is surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the axis of the probe. In another variation of the probe that provides for effective outward radiation of energy or heating, a portion or portions of the outer conductor can be selectively removed. This type of construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna. Another variation on the microwave probe involves having the tip formed in a uniform spiral pattern, such as a helix, to provide the necessary configuration for effective radiation. This variation can be used to direct energy in a particular direction, e.g., perpendicular to the axis, in a forward direction (i.e., towards the distal end of the antenna), or combinations thereof.

Invasive procedures and devices have been developed in which a microwave antenna probe may be either inserted directly into a point of treatment via a normal body orifice or percutaneously inserted. Such invasive procedures and devices potentially provide better temperature control of the tissue being treated. Because of the small difference between the temperature required for denaturing malignant cells and the temperature injurious to healthy cells, a known heating pattern and predictable temperature control is important so that heating is confined to the tissue to be treated. For instance, hyperthermia treatment at the threshold temperature of about 41.5° C. generally has little effect on most malignant growth of cells. However, at slightly elevated temperatures above the approximate range of 43° C. to 45° C., thermal damage to most types of normal cells is routinely observed. Accordingly, great care must be taken not to exceed these temperatures in healthy tissue.

At the beginning of an ablation procedure, the water content of targeted or surrounding tissue may desirably enhance the dielectric coupling between a microwave antenna and surrounding tissue. However, as ablation proceeds, the water content of surrounding tissue may decrease due to, for example, thermal desiccation or dehydration, which negatively affects dielectric coupling between a microwave ablation antenna and targeted or surrounding tissue. In certain instances, uneven or undesirable ablation patterns may form as a result thereof, which may lead to uneven or incomplete heating within the targeted tissue, which may, in turn, lead to complications and impaired operative outcomes. Further, many types of malignancies are difficult to reach and treat using non-invasive techniques or by using invasive antenna probes designed to be inserted into a normal body orifice, e.g., an easily accessible body opening. These types of conventional probes may be more flexible and may also avoid the need to separately sterilize the probe; however, they are structurally weak and typically require the use of an introducer or catheter to gain access to within the body. Moreover, the addition of introducers and catheters necessarily increase the diameter of the incision or access opening into the body thereby making the use of such probes more invasive and further increasing the probability of any complications that may arise.

Structurally stronger invasive probes exist and are typically long, narrow, needle-like antenna probes which may be inserted directly into the body tissue to directly access a site of a tumor or other malignancy. Such rigid probes generally have small diameters that aid not only in ease of use but also reduce the resulting trauma to the patient. A convenience of rigid antenna probes capable of direct insertion into tissue is that the probes may also allow for alternate additional uses given different situations. However, such rigid, needle-like probes may experience difficulties in failing to provide uniform patterns of radiated energy; and may fail to provide uniform heating axially along and radially around an effective length of the probe. Accordingly, it may be difficult to otherwise control and direct the heating pattern when using such probes.

Additionally, a dielectric junction used to separate portions of a rigid probe may be subjected to bending, compression, and rotational forces during manufacture, and during use. These forces may lead to failure of the junction, particularly where the dielectric junction includes an integrally formed coupling member, such as a threaded or ribbed section. This effect is exacerbated by the structural properties of conventional dielectric materials, such as porcelain or other ceramic materials, which tend to be brittle.

SUMMARY

The present disclosure provides a surgical microwave antenna assembly, methods of use therefor, e.g., in microwave antenna assemblies used in tissue ablation applications, and methods of manufacture thereof. In some variations, the microwave antenna assembly has proximal and distal radiating portions. A coupler, or puck, may be a junction member that couples the proximal and distal radiation sections. At least a portion of the coupler may be disposed between the proximal and distal radiating portions. The distal end of the distal radiating portion may include a trocar having a tapered end which terminates at a tip configured to allow for the direct insertion into tissue with minimal resistance. An inner and an outer conductor extend through the proximal radiating portion, with the inner conductor disposed within the outer conductor. The inner conductor may extend through a channel disposed longitudinally in the coupler assembly. The inner conductor may further extend at least partially into the distal radiating portion. The microwave antenna assembly includes a coolant chamber disposed within the trocar that is configured to receive a cooling fluid, such as water, via a coolant inflow tube in fluid communication with a source of cooling fluid. The microwave antenna assembly may also be connected to a source of microwave energy.

The puck may be formed from elastomeric or ceramic dielectric material. In some embodiments, the puck may be formed from an unbreakable thermoplastic elastomer, such as without limitation, polyether block amide, such as Pebax®, manufactured by The Arkema Group of Colombes, France; polyetherimide (PEI), such as Ultem® and/or Extem®, manufactured by SABIC Innovative Plastics of Saudi Arabia; polyimide-based polymer, such as Vespel®, manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., United States. In some embodiments, the puck may be formed from ceramic. In some embodiments, tension is applied to the inner conductor, which in turn places the puck in a state of compression, resulting in improved strength and stiffness of the antenna assembly.

The proximal and distal radiating portions may include a dielectric coating formed from, for example without limitation, a heat resistant ceramic material such as titanium dioxide and/or zirconium dioxide. During a microwave ablation procedure, desiccation of target and/or surrounding tissue may adversely affect the electrical properties at the surgical site, including without limitation, causing impedance mismatching and/or undesirable ablation volumes. The dielectric coating may reduce the detrimental effects of tissue desiccation on the ablation process, and may improve operative outcomes and decrease patient recovery times.

In an embodiment according to the present disclosure, a surgical antenna assembly includes a coaxial feedline having an inner conductor, an outer conductor, and a dielectric disposed therebetween. A trocar screw having a distal threaded section and a cylindrical proximal section is operably electrically coupled to a distal end of the inner conductor. The cylindrical proximal section may include a threaded section. A puck is integrally formed with the trocar screw cylindrical proximal section, by, for example without limitation, overmolding, to form the trocar screw/puck subassembly. The surgical antenna assembly includes an electrically conductive distal radiating section having a distal tapered end and a proximal cylindrical end. In embodiments, the distal radiating section has a generally cylindroconical shape. A cooling chamber is defined within the distal radiating section, having an opening to the proximal end of the distal radiating section and having a threaded section into which is threaded the trocar screw. The disclosed antenna includes a proximal radiating section operably coupled to the outer conductor of the feedline. The proximal radiating section may have a generally cylindrical shape. Additionally or alternatively, the proximal radiating section may have a generally square or hexagonal cross sectional shape. The inner conductor is placed under tension and fastened, which draws together the distal radiating section, the trocar screw/puck subassembly, and the proximal radiating section, to form the antenna assembly. In an embodiment, a tensioning mechanism is generally coupled to the inner conductor. Movement of the tensioning mechanism draws the distal radiating section, the puck, and the proximal radiating section under compression to stiffen the antenna assembly.

In an embodiment, the puck includes a distal puck section, a central puck section, and a proximal puck section. The outer diameter of the central puck section is greater than that of at least one of the outer diameter of the distal puck section and the outer diameter of the proximal puck section. The outer diameter of the central puck section is about equal to the outer diameter of the proximal cylindrical end of the distal radiating section and/or the outer diameter of the proximal radiating section.

In an embodiment, the disclosed surgical antenna includes an outer jacket surrounding at least one of the distal radiating section, the puck, and the proximal radiating section. The outer jacket is formed from polytetrafluoroethylene (PTFE), such as Teflon®, or any suitable lubricious polymer such as polyethylene terephthalate (PET) or polyimide. The outer jacket may enable the antenna assembly to more easily penetrate tissue by reducing friction between the shaft and tissue, and/or by inhibiting the adhesion of biomaterials to the shaft.

Also disclosed is a method for manufacturing a surgical antenna. The disclosed method includes the steps of providing a trocar screw adapted to receive a conductor at the proximal end thereof and bonding a conductor to the trocar screw to form a trocar screw subassembly. The conductor may be coupled to the trocar screw using any suitable manner of electrically-conductive bonding, for example without limitation, welding, brazing, soldering, and crimping. The trocar screw subassembly may then be positioned into a mold that is configured to overmold a puck on the trocar screw subassembly. Puck material, for example and without limitation, Pebax®, Ultem®, Extem®, Vespel® and/or ceramic, is injected into the mold and allowed to set, forming a puck assembly. The puck assembly is released from the mold. A trocar adapted at the proximal end thereof to couple to the trocar screw is provided, and coupled to the trocar screw (e.g., by screwing the trocar onto the trocar screw) to form a distal radiating section. A proximal antenna member adapted at the distal end thereof to couple to the puck assembly is provided, and coupled to the puck assembly such that the conductor passes longitudinally through the proximal antenna member and exits at a proximal end thereof. The conductor is tensioned to draw together the distal radiating section, puck assembly, and proximal antenna member under compression to form an antenna assembly, and the conductor is fixed in relation to the proximal antenna member in order to maintain the stiffness of the antenna assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a representative diagram of a variation of a microwave antenna assembly in accordance with an embodiment of the present disclosure;

FIG. 2 shows an cross-sectional view of a representative variation of a distal end of microwave antenna assembly in accordance with an embodiment of the present disclosure;

FIG. 3 shows a cross-sectional view of a representative variation of a proximal end of microwave antenna assembly in accordance with an embodiment of the present disclosure;

FIGS. 4A-4D show perspective views of a embodiment of a distal portion of a microwave antenna in various stages of assembly in accordance with an embodiment of the present disclosure;

FIG. 5 shows a perspective view of an embodiment of a microwave antenna coupler having a tensioned inner conductor in accordance with an embodiment of the present disclosure; and

FIGS. 6A-6B show cross-sectional views of a distal end of a microwave antenna in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure will be described herein with reference to the accompanying drawings. As shown in the drawings and as described throughout the following description, and as is traditional when referring to relative positioning on an object, the term “proximal” refers to the end of the apparatus that is closer to the user and the term “distal” refers to the end of the apparatus that is further from the user. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

FIG. 1 shows an embodiment of a microwave antenna assembly 100 in accordance with the present disclosure. The antenna assembly 100 includes a radiating portion 12 that is connected by feedline 110 (or shaft) via cable 15 to connector 16, which may further connect the assembly 10 to a power generating source 28, e.g., a microwave or RF electrosurgical generator. Assembly 100, as shown, is a dipole microwave antenna assembly, but other antenna assemblies, e.g., monopole or leaky wave antenna assemblies, may also utilize the principles set forth herein. Distal radiating portion 105 of radiating portion 12 includes a tapered end 120 which terminates at a tip 123 to allow for insertion into tissue with minimal resistance. It is to be understood, however, that tapered end 120 may include other shapes, such as without limitation, a tip 123 that is rounded, flat, square, hexagonal, or cylindroconical.

An insulating puck 130 is disposed between distal radiating portion 105 and proximal radiating portion 140. Puck 130 may be formed from any suitable elastomeric or ceramic dielectric material by any suitable process. In embodiments, the puck 130 is formed by overmolding from polyether block amide (e.g., Pebax®), polyetherimide (e.g., Ultem®and/or Extem®), polyimide-based polymer (e.g., Vespel®), or ceramic. As best illustrated in FIG. 2, puck 130 includes coolant inflow port 131 and coolant outflow port 133 to respectively facilitate the flow of coolant into, and out of, coolant chamber 148 of trocar 122 as further described hereinbelow.

With reference now to FIGS. 2, 3, and 4A-4D, distal radiating portion 105 includes a trocar 122 having a generally cylindroconical shape. Proximal radiating portion 140 includes a proximal antenna member 128 having a generally cylindrical shape. Additionally or alternatively, proximal antenna member 128 may have a generally square or hexagonal shape. Trocar 122 and proximal antenna member 128 may be formed from a variety of biocompatible heat resistant conductive material suitable for penetrating tissue, such as without limitation, stainless steel. Antenna assembly 110 includes a coaxial transmission line 138 having, in coaxial disposition, an inner coaxial conductor 150, an intermediate coaxial dielectric 132, and an outer coaxial conductor 134. Nominally, coaxial transmission line 138 has an impedance of about 50 ohms. Inner coaxial conductor 150 and outer coaxial conductor 134 may be formed from any suitable electrically conductive material. In some embodiments, inner coaxial conductor 150 is formed from stainless steel and outer coaxial conductor 132 is formed from copper. Coaxial dielectric 132 may be formed from any suitable dielectric material, including without limitation, polyethylene terephthalate, polyimide, or polytetrafluoroethylene (PTFE) (e.g., Teflon®, manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., United States). Inner coaxial conductor 150 is electrically coupled with trocar 122. Outer coaxial conductor 134 is electrically coupled to proximal antenna member 128.

A longitudinal opening 146 within trocar 122, and open to a proximal end thereof, defines a cooling chamber 148 and a threaded section 145 within trocar 122. Cooling chamber 148 may have a generally cylindrical shape and, additionally or alternatively, may have a stepped, tapered, conical, or other shape that is generally dimensioned in accordance with the shape of the tapered end 120 of the cylindroconical profile of trocar 122 to permit the flow of coolant to more effectively reach the distal regions of trocar 122. Additionally or alternatively, cooling chamber may have a square, hexagonal, or any suitable shape. Additionally, the dielectric properties of sterile water or saline flowing through cooling chamber 148 may enhance the overall ablation pattern of antenna 100. A coolant inflow tube 126 is in operable fluid communication at a proximal end thereof with a source of cooling fluid (not explicitly shown), and, at a distal end thereof, coolant inflow tube 126 is in fluid communication with cooling chamber 146 to provide coolant thereto. Coolant inflow tube 126 may be formed from any suitable material, e.g., a polymeric material, such as without limitation, polyimide. In an embodiment, coolant inflow tube 126 passes through coolant inflow port 131. In some embodiments, a coolant outflow channel 136 may be provided to facilitate removal of coolant from cooling chamber 146, through antenna assembly 100, to a collection reservoir (not explicitly shown). The coolant may be any suitable fluid, such as without limitation water, sterile water, deionized water, and/or saline.

Threaded section 145 of trocar 122 is configured to receive trocar screw 144. Trocar screw 144 includes at the proximal end thereof an opening 143 defined therein that is configured to accept the distal end of inner coaxial conductor 150. In embodiments, distal end of inner coaxial conductor 150 is fixed within opening 143 by any suitable manner of electromechanical attachment, such as without limitation welding, brazing, and/or crimping. As seen in FIG. 4A, an inflow groove 147 and an outflow groove 149 are disposed longitudinally through the threaded portion of trocar screw 144 to respectively facilitate the flow of coolant into, and out of, cooling chamber 148. Inflow groove 147 and outflow groove 149 may be configured to accommodate the insertion of coolant inflow tube 126 and/or a corresponding outflow tube (not explicitly shown). A return path 156 in the antenna assembly may additionally or alternatively provide an exit conduit for the cooling fluid.

In the illustrated embodiment, trocar 122 and proximal antenna member 128 include a dielectric coating 121, 127, respectively, on the respective outer surfaces thereof. The dielectric coating 121, 127 may include any suitable dielectric material, such as without limitation, ceramic material. In some embodiments, dielectric coating 121, 127 may be formed from titanium dioxide and/or zirconium dioxide. Dielectric coating 121, 127 may be applied to trocar 122 and/or proximal antenna member 128 by any suitable process, for example without limitation, plasma spraying or flame spraying. In embodiments, dielectric coating 121, 127 has a thickness in the range of about 0.005 inches to about 0.015 inches. During an ablation procedure, the dielectric coating 121, 127 may provide improved dielectric matching and/or improved dielectric buffering between the antenna and tissue, which may enable the use of higher power levels, which, in turn, may enable a surgeon to achieve greater ablation rates resulting in increased ablation size, reduced operative times, and/or improved operative outcomes.

An outer jacket 124 is disposed about the outer cylindrical surface of antenna assembly 100, e.g., the distal radiating portion 105, puck 130, and proximal radiating section 140. Outer jacket 124 may be formed from any suitable material, including without limitation polymeric or ceramic materials. In some embodiments, outer jacket 124 is formed from PTFE. Outer jacket 124 may be applied to antenna assembly 100 by any suitable manner, including without limitation, heat shrinking.

Continuing with reference to FIGS. 4A-4D, a method of manufacturing antenna assembly 100 is disclosed wherein inner coaxial conductor 150 is inserted into opening 143 of trocar screw 144. Inner coaxial conductor 150 is electrically fixed to trocar screw 144 by any suitable manner of bonding, such as without limitation, laser welding, brazing, or crimping. The coaxial transmission line 138 and trocar screw 144 subassembly is placed in a mold (not explicitly shown), such as without limitation an injection micro-mold, that is configured to overmold the puck 130. Advantageously, inflow groove 147 and outflow groove 149 are aligned with mold features (not explicitly shown) corresponding to coolant inflow port 131 and coolant outflow port 133 such that, when molded, a continuous fluid connection is formed between inflow groove 147 and coolant inflow port 131, and between outflow groove 149 and outflow port 133.

Puck material, e.g., ceramic, Pebax®, Ultem®, Extem®, Vespel®, or any suitable polymer having dielectric properties, is shot into the mold, allowed to cool/and or set, and subsequently released from the mold to form an assembly that includes puck 130, trocar screw 143 and coaxial transmission line 138 as best illustrated in FIG. 4B. The formed puck 130 includes a center section 137 having an outer diameter corresponding to the outer diameters of trocar 122 (inclusive of the thickness of dielectric coating 121) and/or proximal antenna member 128 (inclusive of the thickness of dielectric coating 127). Puck 130 further includes a distal shoulder 141 having an outer diameter corresponding to the inner diameter of trocar 122, and a proximal shoulder 139 having an outer diameter corresponding to the inner diameter of proximal antenna member 128.

Trocar 122 may then be threaded onto trocar screw 144 to form the distal radiating section 120, as best shown in FIG. 4C. Inflow tube 126 may then be inserted into coolant inflow port 131. Proximal antenna member 128 may then be positioned against puck 130 such that the distal end of proximal antenna member 128 engages the proximal shoulder of puck 130, thus forming a sealed proximal radiation section 140.

Tension may be applied to inner coaxial conductor 150 and/or dielectric 132 in a proximal direction, thereby drawing together distal radiating section 105, puck 130, and proximal radiating section 140, and placing puck 130 in a state of compression. Inner coaxial conductor 150 and/or dielectric 132 may be fixed in a state of tension at an anchor point 151, by any suitable manner of fixation, including without limitation spot welding, brazing, adhesive, and/or crimping. In this manner, the antenna sections are “locked” together by the tensile force of inner coaxial conductor 150 and/or dielectric 132, which may result in improved strength and stiffness of the antenna assembly.

Outer jacket 124 may be applied to the outer surface of radiating portion 12 by any suitable method, for example without limitation, heat shrinking, overmolding, coating, spraying, dipping, powder coating, baking and/or film deposition.

It is contemplated that the steps of a method in accordance with the present disclosure can be performed in a different ordering than the ordering provided herein.

Turning now to FIGS. 6A and 6B, views of a distal end of a microwave antenna in accordance with an embodiment of the present disclosure are presented wherein FIG. 6A illustrates a cross-sectional view taken in a plane which exposes, inter alia, coolant inflow tube 126 and coolant outflow channel 136. FIG. 6B exposes a plane oriented approximately perpendicular to that of FIG. 6A, which illustrates, inter alia, a relationship between trocar screw 144, inner conductor 150, and puck 130.

The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Further variations of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be made or desirably combined into many other different systems or applications without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law. 

1. A method of manufacturing a surgical antenna, comprising the steps of: providing a trocar screw adapted to receive a conductor at the proximal end thereof; electrically bonding a conductor to the trocar screw; positioning the trocar screw into a mold configured to overmold a puck thereupon; injecting puck material into the mold; allowing the puck material to set to form a puck assembly; releasing the puck assembly from the mold; providing a trocar adapted at the proximal end thereof to couple to the trocar screw; electrically coupling the trocar to the trocar screw to form a distal radiating section; providing a proximal antenna member adapted at the distal end thereof to couple to the puck assembly; and coupling the proximal antenna member to the puck assembly such that the conductor passes longitudinally through the proximal antenna member and exits at a proximal end thereof.
 2. The method in accordance with claim 1, further comprising the steps of: tensioning the conductor to draw together the distal radiating section, puck assembly, and proximal antenna member under compression to form an antenna assembly; and fixing the conductor in relation to the proximal antenna member to maintain the stiffness of the antenna assembly.
 3. The method in accordance with claim 1, wherein the bonding of the conductor to the trocar screw is achieved by at least one of welding, soldering, and crimping.
 4. The method in accordance with claim 1, wherein the mold is further configured to form at least one of an inflow groove and an outflow groove in the puck assembly.
 5. The method in accordance with claim 4, further comprising the step of inserting an inflow tube into an inflow slot.
 6. The method in accordance with claim 4, further comprising the step of inserting an outflow tube into an outflow slot.
 7. The method in accordance with claim 1, further comprising the step of applying an outer jacket to the antenna assembly. 